Magnetic flux regulator



Patented Sept. 22, 1942 UNITED STATES PATENT OFFICE MAGNETIC FLUX REGULATOR Rene A. Braden, Collingswood, N. J., assignor to Radio Corporation of America, a corporation of Delaware 8 Claims.

This invention relates to regulating systems and more particularly to a system for producing a constant magnetic eld and for overcoming the effect of hysteresis in an electromagnet, particularly in connection with a magnetron oscillator or the like.

It is well known to those skilled in the art that the curve representing the magnetic flux produced by an electromagnet as a function of the energizing current is a closed loop, commonly known as the hysteresis loop. For a given value of energizing current, the iiux intensity may have any value between two limits iixed by the hysteresis curve, and will actually have a value which depends on the direction in which the energizing axial magnetic eld which determines the frequency and amplitude of a magnetron oscillator, it is not sufficient merely to control the amplitude of the energizing current, since the magnetic flux is not wholly dependent upon the arnplitude of the energizing current.

In order to attain a satisfactory degree of stability, both as to frequency and amplitude with a magnetron oscillator, it is therefore desirable to provide a system in which the magnetic .flux itself is held constant. In accordance with this invention, the control of the magnetic ux density is effected by superimposing an alternating current component on the energizing current and gradually reducing its amplitude so that for a given value of energizing current the electromagnet will operate at a predetermined point on its hysteresis curve.

Among the objects of this invention are the provision of means for regulating the magnetic uX density of an electromagnet; the provision of means for superimposing an alternating current on the direct magnetizing current in order to minimize the hysteresis effect; the provision of an improved stabilized magnetron oscillator; the provision of means for automatically decreasing the amplitude of a superimposed alternating current; and means for periodically applying such a correcting current at predetermined intervals to permit uninterrupted operation of the magnetron oscillator during certain periods While a correcting current is applied to the electromagnet during intermediate periods.

This invention will be better understood from the following description when considered in connection with the accompanying drawing in which Figure l represents a manually operated system in accordance with this invention; Figure 2 is an alternative manually operated system; Figure 3 is a manually operated modication in which the correcting current is applied directly to the magnetizing current regulator; Figure 4 is a system in which a correcting Wave train is automatically produced; and Figure 5 represents a television transmitter utilizing a magnetron oscillator in which the magnetic eld is corrected during the radiation of synchronizing impulses.

While the present invention is described in connection with a magnetron oscillator, it is not limited to such use. The system herein to be disclosed is applicable to control the intensity of a magnetic vi-leld whenever it is necessary or desirable to maintain the iiux density at an accurately predetermined value.

Referring to Fig, 1, a magnetron oscillator or detector is indicated diagrammatically by rectangle 1. An electromagnet 9, comprising a permeable core il and an energizing winding I3 is arranged so as to produce the necessary axial eld through the magnetron. The energizing winding I3 is connected to a source of current which may be a battery I5 or the like through an adjusting resistor l'l and through a portion of a potentiometer I9, the outer terminals of which are connected to the secondary of a transformer 2|. 'The primary of the transformer 2l is connected to any suitable source of alternating current.

In operation, the device described above is iirst adjusted by means of resistor l1 so that approximately the desired field intensity is obtained. The resistance of potentiometer IQ is preferably low with respect to that of resistor I'l. An alternating current is applied to transformer 2i, and the Contact arm 23 of potentiometer i9 is placed so as to insert a substantial alternating current in series with the magnetizing current from the battery I5. Contact 23 is then slowly moved towards position A on the potentiometer. When position A is reached, the alternating voltage component has been reduced to zero and, due to the gradual decrease of the superimposed alternating current, the electromagnet 9 is made to operate at a given point on its hysteresis curve. Whenever the direct magnetizing vcurrent is changed, this process may be repeated and the hysteresis error corrected in the manner described.

Fig. 2 is a modification of Fig. l in which separate current paths are provided for the direct energizing current from the battery set i5 and for the alternating component. A separate winding 25 on the electromagnet core ll is provided. This winding is connected to the potentiometer I9, which is connected across transformer 2l as before. The operation of this modication is the same as that described with respect to Fig. 1. Its advantage lies in the fact that adjustments of the potentiometer I9 do not effect the direct current flowing through the energizing winding I1.

Referring now to Fig. 3, a preferred embodiment is illustrated in which the alternating control potentiometer is applied to impress an alternating component on a regulated direct current energizing source, which may operate in conjunction with a rectifier or other well known direct current source. For example, a source of rectified direct current is connected to a pair of terminals 22, 24, across which a regulating neon tube 26 is connected through a limiting resistor 3B. Current for the magnetizing coil l1 is supplied to the source through a serially connected regulating tube 29 and a potentiometer 3i. The cathode of a first amplifier 21 is connected to a point on potentiometer 3l and its control grid to the high voltage terminal of neon tube 26. The eiiective grid bias of the tube, therefore, varies as a function of the load current through the potentiometer. A second or reversing amplifier 28 is connected between the rst amplifier and the regulating tube so that the cathode to grid voltage of the regulating tube 29 is equal to the drop in the second ampliiier plate resistor 32. Thus, an increase in load current increases the positive potential of the cathode of the rst amplifier, which decreases the plate current of the lirst amplifier. As a result the grid of the reversing amplier becomes more positive and its plate voltage, and thus the grid of the regulating tube, become less positive. Consequently, the impedance of the regulating tube increases and overcomes the original increase in load current.

It is to be noted that the grid bias of the first amplifier tube 2S is obtained through a Connection which includes a potentiometer I9, the terminals of which are connected to a source of alternating current such as transformer 34. By Varying the position of the contact arm 23 of potentiometer i9 an alternating current component may be impressed on the system, and by manipulating the potentiometer in the manner described above, the hysteresis effect of the electromagnet may be Overcome.

Fig. 4 shows a further modification of this invention in which automatic operation is achieved so that it is no longer necessary to manually operate a potentiometer in order to adjust the system. In accordance with this modification of my invention a damped sine wave impulse is generated by a thermionic tube 33. The grid of this tube is normally biased beyond plate current cut-oli, by means of a battery 35. A battery 3l of opposed potential is adapted to be connected to the grid through a push button 39. The plate circuit of tube 33 contains a resonant tank circuit comprising an inductor il and a capacitor 43. Anode potential is supplied by a battery 45.

To operate the device which has been described so far, push button 39 is momentarily depressed, and the resulting positive potential which is applied to the grid of tube 33 allows a momentary current to flow through the tank circuit. As a result, the tank circuit is momentarily excited so that a brief oscillatory wave train is generated, the amplitude of which gradually dies away. Such a damped wave train is the equivaient of the alternating current of decreasing amplitude which was obtained manually by operating the potentiometer I9 illustrated in Figs. 1 to 3. By superimposing this damped alternating voltage on the grid of the iirst control ampliiier tube 21 a corresponding damped wave train is momentarily passed through the energizing winding of the electromagnet l1 to overcome the hysteresis eifect in the manner described above. 'Ihat portion of Fig. 4 between the vertical dash lines corresponds to the similar portion of the circuit of Fig. 3, and differs therefrom by the substitution of the damped wave generator for the alternating voltage source 34. The D. C. voltage source for operating the control tubes and magnetron has not been illustrated in Fig. 4, nor has the complete control circuit, since neither of these elements, per se, are a part of the present invention. It is to be understood, however, that such a source of voltage is provided and that the rst amplier 21 of Fig. 4 is coupled to the regulating tube 29 by means of a reversing ampliiiela 28 as illustrated in Fig. 3. The purpose of the reversing amplifier is to provide the pro-per direction of control to make the regulating tube oppose and not aid changes in load current.

In some instances, it is desirable to provide continuous automatic correction for the automatic field. In order to accomplish this, the push `button of Fig. 4 is replaced by a device which impresses short positive impulses on the grid of tube t3. In such an instance it is, of course, necessary to so select the time of occurrence of the correcting impulses so that they do not disturb normal transmission or reception. For example, if the electromagnet is used in conjunction with a magnetron oscillator which is modulated in the audio range, the control impulses which are applied to the magnetic field may be made to occur at superaudible frequency.

Fig. 5 represents an arrangement in which automatic correction is obtained in connection with a television transmitter. In accordance with this modification of my invention, the magnet correction is made to coincide in time with the synchronizing impulses. The magnetron oscillator il is connected to an antenna 49 in the usual manner. For the sake of stability a regulated lament supply 5l and a regulated anode supply 53 are employed to energize their corresponding electrodes. The regulated magnet supply 55 corresponds to the modified direct current regulating source illustrated in the righthand portion of Fig. 4. damped wave generator 5i corresponding to the generator likewise described above in connection with Fig. 4, except that push button 39 is replaced by a control impulse which is derived from a synchronizing generator 59. The synchronizing generator is also used to modulate the output of oscillator 41 as is well known.

I claim as my invention:

1. The method of stabilizing a radio device including an electromagnet having a magnetizable metallic core the flux density of which determines the operating characteristics of said device which includes the steps of passing a direct energizing current through said electromagnet, passing an alternating current of a predetermined frequency through said electromagnet, and gradually reducing the amplitude of said alter- It is energized by a nating current to condition said electromagnet for operation at a predetermined point on its hysteresis loop characteristic.

2. The method of stabilizing a radio device at least one of whose operating characteristics is determined by the iiux density of an electromagnet having a magnetizable metallic core which includes the steps of passing a regulated direct current through said electromagnet, superimposing on said direct current at required intervals an alternating current of predetermined frequency, and gradually reducing the amplitude of said alternating current component to zero to permit continued operation on a predetermined point of the hysteresis curve of said electromagnet. 1

3. In a radio device, the combination which includes a magnetron, an electromagnet for producing a magnetic field for energizing said magnetron, said electromagnet including a magnetizable metallic core, means for producing a normal magnetizing current, means for passing said magnetizing current through said electromagnet, and means for establishing a unique relation between the magnetic eld strength and the amplitude of said magnetizing current, said means including means for passing an alternating current of predetermined frequency through said electromagnet, and means for gradually reducing the amplitude of said alternating current to determine the operating point of said electromagnet at a predetermined point on its hysteresis curve.

4. The combination which includes an electromagnet having a magnetizable metallic core, a magnetron located in the field of Said electromagnet means for producing a magnetizing current, means for regulating the amplitude of said current to maintain said magnetizing current at a desired value, means coupled to said regulating means for varying the amplitude of said magnetizing current to thereby impress an alternating current component on said magnetizing current, and means for gradually reducing to zero the amplitude of said component to establish a unique relation between said magnetizing current and said eld.

5. In combination, an electromagnet having a magnetizing Winding and a permeable core of magnetizable metal, a magnetron located in the field of said magnet means for producing a direct energizing current of normally constant amplitude the amplitude of which determines the operating conditions cf said magnetron, and means including an oscillator for impressing at will cn said direct energizing current an alternating current component comprising a single wave train of alternating impulses of decreasing arnplitude whereby the eiect of the hysteresis cf said core on the flux density is minimized.

6. In combination, an electromagnet having a magnetizing winding and av magnetizable metallic core, means for producing a direct energizing current of normally constant amplitude, and means including a keyed oscillator for impressing on said direct energizing current an alternating component comprising a single damped wave train of alternating current vwhereby the effect of the hysteresis of said core on the iluX density of said electromagnet is minimized.

7. In combination, a magnetron oscillator, an electromagnet including a magnetizable metallic core for producing an axial iield in said oscillator, means for producing a constant amplitude energizing current for said electromagnet, means for modulating said magnetron by signal representing voltages, and means for superimposing on said energizing current a component comprising a single damped Wave train of alternating current to establish a unique relation between the flux density of said electromagnet and said energizing current.

8. In a radio device, the combination including an electromagnet having a permeable metallic core, means including a constant magnetizing current for producing a magnetic field, an oscillating electron discharge device in said field, the intensity of said eld controlling an operating characteristic of said device, means for modulating said oscillating discharge device by signal representing voltages, and means for establishing a unique relation between the intensity of said eld and the amplitude of said magnetizing current.

RENE A. BRADEN. 

